1. When threatened by sexual assault, ovulating women display a measurable increase in physical strength. In 2002, SUNY-Albany psychologists Sandra Petralia and Gordon Gallup had 192 female undergraduate students read a story about either a female character being stalked by a suspicious male stranger in a parking lot (ending with: "As she inserts the key into her car door she feels his cold hand on her shoulder …") or a similar story in which the female character is surrounded by happy people on a warm summer's day (ending with: "She starts her car, adjusts the stereo, and as she pulls out of the parking lot those nearby can hear her music blasting"). The researchers measured the handgrip strength of each participant before and after she read the story, and compared the scores. Petralia and Gallup also knew from the results of a urine-based ovulation test kit where in their reproductive cycles each participant was, so the researchers could differentiate among women in the menstrual, follicular, ovulatory, and luteal phases. A fifth group consisted of those women who were on contraceptives at the time of the study. The results were unambiguous: Only the ovulating women who read the sexual assault scenario exhibited an increase in handgrip strength. Ovulating women who read the control passage and nonovulatory women who read the sexual assault material grasped with the same intensity as before.
2. Ovulating women overestimate strange males' probability of being rapists. Add this one to a growing list of adaptive cognitive biases—evolved psychological distortions that orient people toward strategic decision-making. These findings come from a 2007 report by Christine Garver-Apgar and her colleagues. "When the costs of being sexually victimized are highest," reason these investigators, "women should shift their perceptions to decrease false negative errors at the expense of making more false positive errors. Thus, we predicted that women perceive men as more sexually coercive at fertile points of their cycle than at non-fertile points." The researchers showed 169 normally ovulating women videotaped interviews with various men and asked them to rate the men on several dimensions, including their tendencies toward sexual aggression, kindness, or faithfulness. The more fertile the woman was at the time of her judging, the more likely she was to describe the men as "sexually coercive." Ovulating women didn't see these men as being less kind, faithful, or likely to commit—only more inclined to rape them.
3. Ovulating women play it safe by avoiding situations that place them at increased risk of being raped. Fending off would-be rapists and pigeonholing strange men as potential sex fiends sounds exhausting—wouldn't it make more sense to avoid dangerous places and unknown males altogether? That is exactly what ovulating women tend to do. At least two studies have demonstrated that women at the peak of their fertility are less likely than their peers to have engaged in high-risk activities such as walking alone in a park or forest, letting a stranger into the house, or stopping their cars in a remote place over the preceding 24 hours. Importantly, as German investigators Arndt Bröder and Natalia Hohmann established, ovulating women are not less active in general—they're still busy shopping, going to church, visiting friends, and so on—but they avoid doing those things that make them sexually vulnerable.
4. Women become more racist when they're ovulating. At least white American ovulating women do when it comes to thinking about black American men. Those are the jaw-dropping, politically incorrect findings of Michigan State University's Carlos Navarrete and colleagues. White, undergraduate females were evaluated for race bias using several variants of an implicit association test, which asks participants to perform a word-matching task that indicates the relative accessibility of certain stereotypes. The women who happened to be ovulating scored especially high when it came to fear of black (as opposed to white) men, a fact that the authors interpret as reflecting an evolved disposition to avoid so-called "out-group males," who "may not have been subject to the same social controls as in-group members and would have constituted a threat in antagonistic situations." In this case, skin color serves as a convenient marker of group identity. (The authors concede that people of different skin colors came into contact with one another only in recent times, evolutionarily speaking, but propose that any physical trait that serves to demarcate an out-group member would be processed by ovulating females as a sort of "hazard heuristic.") Stereotypes about the particular out-group being prone to violence may also play a role, so, at least in American society, cultural transmission works alongside evolutionary biology in promoting racism. It remains unclear if the same race bias occurs in ovulating women from other races: Do black women show heightened fear of white men?
I don't know about you, but I'm riveted, and convinced, by much of the logic in this anti-rape area. And researchers are just getting started. Above is a set of astonishing truths that, had an evolutionary approach to studying complex social behavior not been adopted so rigorously over the past quarter-century and applied to human sexuality, would have gone entirely unnoticed—not least of which by a Kinsey-6 gay man who wouldn't know what to do with an ovulating woman if she came with instructions.